1. Field of the Invention
The present invention relates to a radio receiver and more particularly to a CMA (constant modulus algorithm)-based antenna system.
2. Description of the Prior Art
If the amplitude of transmitted electromagnetic wave is constant as in case of, for example, frequency or phase modulated wave, then applying the CMA (constant modulus algorithm) to an array antenna system provides one of successful solutions to the problem of multipath errors. In the CMA, the weighting circuits connected with respective antennas are so controlled as to make constant the amplitude of the synthesized output signal of the adder for adding the weighted signals from the weighting circuits.
However, in the conventional CMA, the output signal may converge with phase differences among the received signals remaining as they are. This is because it is possible to converge the amplitude of the output signal to a predetermined value by increasing gains even if there are phase differences among the received signals from the antennas. Generally, the signal-to-noise ratio of the output signal of the adder decreases with increase in phase differences, becoming the maximum when the phase differences are all 0's.
Further, the conventional CMA can not cope with a case when there is any synchronous error of a symbol level or any delayed wave caused by reflection and diffraction of the transmitted wave because only the signals received at a time are added together in an antenna system provided with a synthesis controller using the conventional CMA.